In this document the following abbreviations are used when describing the prior art and also when describing the present invention:    Balun Balanced to unbalanced transformer,    FR4 Base material for printed circuit boards (FR=Flame Retardant, and Type “4” indicates woven glass reinforced epoxy resin),    IC integrated circuit,    RF radio frequency,
One of the basic tasks in RF-technology is amplification of RF-signals with sufficient bandwidth, with a desired gain, and with sufficient linearity. Also the fact that power losses are sufficiently small is an important issue especially in mobile phone applications. The current tendency is towards smaller systems with respect to physical size, weight, and power consumption. This means that various types of electrical elements handling also analogue RF-signals are included into integrated circuits.
A generally used construction for RF-integrated circuits (RF-IC) having both active electrical elements and low-loss passive electrical elements is such that the active elements have been integrated into a first part of an RF-IC and the passive elements into a second part of an RF-IC. In the continuation of this document the first part and the second part are referred as ‘the active part’ and ‘the passive part’, respectively. The body of the active part may be made, for example, of silicon and the body of the low-loss passive part may be made, for example, of glass. A side view of an exemplary system of this kind is illustrated in FIG. 1. The active part 101 and the passive part 102 are electrically connected with each other via electrically conductive solder bumps 103, 104 and via electrically conductive areas 105 on the base plate 106, i.e. the flip-chip technique. It is also possible to accomplish said electrical connections using some other techniques like e.g. wire bonding. The base plate 106 may be made, for example, of FR4. This whole system may be encased into e.g. a plastic package 109. In this document a system 120 consisted of the parts inside the package 109 plus the package 109 itself is called an RF-IC. The RF-IC is connected with a circuit board 110 (a fraction of that shown in FIG. 1) via solder bumps 107 and 108.